SeisMac Activity I: “Take the pulse of your classroom using SeisMac!”
Version 1.1 – October 21, 2010
Prior Knowledge
Students should already have received instruction on the basic principles of
seismic waves. For ideas on how to provide this instruction please see:
http://web.ics.purdue.edu/~braile/edumod/slinky/slinky4.htm.
Guiding Questions
1. What information does a three-component seismogram express?
2. How can first S and P wave arrivals be identified on a three-component
seismogram?
3. How can first S and P wave arrivals on a three-component seismogram
provide evidence that seismic waves travel a curving path through the Earth?
Materials
 PowerBook (2006 or later), MacBook or MacBook Pro with OS X,
connected to a video projector
 SeisMac http://www.suitable.com/tools/seismac.html
 To calibrate the accelerometer in your computer so that SeisMac works
properly you will also need to download the calibration software from
http://www.suitable.com/tools/seismacalibrate.html
 Sample seismograms from www.iris.edu/eno/SeisMac or select your own
recent event using the Rapid Earthquake Viewer at
http://rev.seis.sc.edu/index.html
 Earthquake video (YouTube) – 1995 Kobe 7.2M
http://www.youtube.com/watch?v=0plbf5w0sbA
Lesson Description: Quick Summary
OPERA
Time (min)
Open
5
Prior knowledge
20
Explore/Explain
Reflect
Apply
Total Time Estimate
15
10
20
90
Teacher Instructions (w/ Potential Questioning Sequences)
Open – 5 Minutes
Project SeisMac onto a screen as students arrive in class. Students will notice a
relationship between the trace on the screen and their actions…. If students do
not notice this relationship, have a volunteer jump up and down and observe the
resulting seismograms.
Prior Knowledge – 20 Minutes
Taxonomy
Knowledge
Question
What kinds of graphs are being
shown on the screen?
Answer
Line graphs
Pause the display on SeisMac using the yellow pause/play
button.
Taxonomy
Comprehensio
n
Comprehensio
n
Question
Can someone help us interpret
these graphs? What information
is being shown across the
bottom? What information is
being shown on the vertical axis?
Answer
The horizontal axis shows the
“real time” from your computer’s
clock. This is displayed in hours,
minutes and seconds. The
vertical axis shows the
acceleration in units of gravity (g).
Activity two focuses on helping
students develop an
understanding and appreciation of
ground acceleration.
Based on this graph, what do you Accept all answers but lead
think this program is designed to students to realize that the
do? What makes you think this? computer and software are
recording the motion of the ground
in their classroom.
Instruct students to create a Circle Map for the term “seismogram” to gain a
sense of their prior knowledge of the subject.
“Circle Maps are tools used to help define a thing or idea. It is used to brainstorm
ideas and for showing prior knowledge about a topic. In the center of the circle,
use words, numbers, pictures, or any other sign or symbol to represent the
object, person, or idea you are trying to understand or define. In the outside
circle, write or draw any information that puts this thing in context.” For more
information go to…
http://www.mdianeharrison.com/Thinking%20Maps.htm
Explore/explain – 15 Minutes
Show video clip (YouTube) of the 1995 Kobe earthquake (7.2M)
http://www.youtube.com/watch?v=0plbf5w0sbA to help establish relevance.
Taxonomy
Application
Question
What do you think the display of
Answer
Accept all answers but lead
Analysis
Analysis
SeisMac might look like if it had
been sitting in that room and
running when that earthquake
occurred?
Why do you think the software
shows three graphs to measure
the motion of the ground?
Propose an experiment that
could be conducted to explain
the three traces
students to understand that the
lines would be very squiggly... one
might even suggest that they may
look like a seismogram!
Accept all answers
Try student experiments or tilt the laptop gently three different ways
First Position (Sitting
normally)
Taxonomy
Analysis
Second Position (Stood
up on edge)
Question
What is the relationship between
these physical motions and the
graph?
Third position (Sitting on
the screen with the
keyboard up.
Answer
Lead students to realize that
motion has three components
(X,Y,Z) and that each is
represented on a separate trace
on the graph. Students might also
note that the harder the shaking,
the higher and lower the line goes
on the graph. Thus there is a
correlation to the amount of
energy released.
Reflect – 10 Minutes
Revisit the circle maps students created for the term seismogram. Use a
different color (pen, pencil or markers) as students update their maps by adding
new information, editing or clarifying existing information, and possibly removing
incorrect or irrelevant information.
Apply - 20 Minutes
Distribute the sample three-component seismogram or one from a recent
earthquake of your own choosing from http://rev.seis.sc.edu/index.html
Taxonomy
Comprehensio
n
Question
How is this graph similar to what
we see on the screen?
Comprehensio
n
Review the axis of the
seismograms with the students
and ask students to pick the P
(first signal to arrive) and S
(second signal) wave arrivals on
the seismogram you distributed.
Comprehensio
n
In which component is most of
the energy for the P wave?... for
the S wave?
Application
Why do you think this is the
case?
Answer
Lead students to understand that
the seismic data is a threecomponent graph similar to the
one produced by SeisMac.
Sample Seismogram #1:
The P wave. best seen in the
vertical component, arrives at
~235 seconds. The S wave, best
seen in the North-South
(horizontal) component, arrives at
~685 seconds.
Most of the energy for the P wave
is generally found in the vertical
component, while most of the
energy for the S wave is generally
found in one of the horizontal
components.
Accept all answers but suggest
that students explore this by trying
to replicate the seismogram by
moving the laptop.
Have a volunteer try to replicate the motion shown in this seismogram by shaking
the laptop. Replicate the motion of the P arrival first, then the motion for the S
arrival, and finally put the two together.
Taxonomy
Comprehensio
n
Application
Question
Can someone summarize how
__________ (student’s name)
had to move the computer for the
P wave?… for the S wave?
Answer
For the P wave, most of the
motion is likely to be seen in one
of the horizontal components. For
the S wave, the majority of the
energy is likely to be seen on the
vertical components.
Based on what you already know Waves from distant earthquakes
follow a curving path through the
about particle motion compared
Earth. As a result they arrive at
to the direction of travel for
seismic stations from below. Since
seismic waves (e.g. particles
the motion of a P wave is in the
move parallel to the direction of
direction the wave travels, for a
wave propagation for P waves),
how did the seismic energy arrive wave coming up from below the
at the station that recorded this
earthquake?”
seismograph station, the motion of
the ground will be mostly vertical
(up and down), with a smaller
amount of motion on the
horizontal components (North and
East). By contrast, since the S
wave motion is perpendicular to
the direction of wave travel, an S
wave coming up under the station
will produce larger motion in a
horizontal direction which may be
some combination of the North
and East component directions,
and smaller motion on the vertical
component.
To connect the seismograms students have studied to actual earthquake ground
motion, re-show the 1995 Kobe earthquake (7.2M) video clip
http://www.youtube.com/watch?v=0plbf5w0sbA and challenge students to
identify the arrivals of the different seismic waves in the video.
Challenge Answer: At about 1 second into the video clip, you see a man who
was laying down suddenly sit up so his head appears in the bottom center of the
screen. He was likely to have been awakened by the P wave. At approximately
4 seconds into the clip, the first horizontal motion begins which is likely to be the
S wave either combined with or very closely followed by the arrival of the surface
waves.
Many thanks to Michael Wysession of Washington University at St. Louis, who
developed the initial conception of this activity.
Sample Three-Component Seismogram – 3/28/05 N. Sumatra M 8.7